1. Field of the Invention
The present invention generally relates to an information management system for updating a file, and more particularly to an online database system in which a large amount of updating occur due to a batch process during the reference to data in an online process.
2. Description of the Related Art
In a prior art online database system, when a batch process which accompanies a large volume of updating during the online process is to be executed, a wait status due to an exclusive control of records or a busy device such as a busy disk is incurred, which affects to a performance of the online process. Accordingly, the online process is stopped at night or during holidays to conduct the batch process. As applications of the batch system, charging systems for electricity, gas, water and telephone utilities have been known. In moving toward the internationalization and total systemization of such utility systems, the 24-hour continuous operation of the online process has rapidly been developed and any chance to stop the online process is being lost. JP-A-3-266046 discloses a method for rapidly accessing a database by duplicating files and alternately switching a reference file and an updating file.
Such a prior art method has the following problems.
The contention between the reference and the updating of the file is eliminated but the execution of the batch process for updating a large volume of data takes a long time because the updating rate remains unchanged.
In addition, because of the data copy process from the updating file to the reference file, the total number of times of input and output of the files is approximately twice as large as that of the ordinary batch process. Further, during the copy process from the updating file to the reference file, there is a high possibility that a device (for example, a disk) for the reference file is busy and a wait status is incurred in the online process of the reference file so that a response time of the online process is deteriorated. A data management system which has a file for storing copies of pages of a file such as a database and extended storage (ES) and when a user application program is to access the file, is first read from the ES and an updated page is output to the ES together with the file is commercially available from Hitachi Ltd. as Model XDM E2.